In the field of micromechanics, mechanical devices are of the scale of micrometers. A suitable power source for supplying continuous rotational motion to other micromechanisms does not currently exist. There are micrometer sized electrostatic micromotors that display rotational motion but are unable to drive a mechanical load. This is due to several reasons which chief among them is the inability to produce an output shaft from the micromotor. Furthermore, there is great difficulty in connecting a mechanical load to the perimeter of the rotor itself because the location of stators which are used to electrostatically or electromagnetically drive the device, interfere with external connections.
FIG. 1 illustrates a prior art micromotor that suffers from the above described limitations. As explained in Mehregany et at., "Friction and Wear in Microfabricated Harmonic Side-Drive Motors", IEEE Solid State Sensor and Actuator Workshop, Hilton Head Island, S.C., June 4-7, IEEE Catalogue No. 90CH2783-9, pages 17-22, the prior art provides a micromotor including a rotor pinned to a substrate or stator by a central bearing that restricts its lateral and axial motion. The entire structure shown in the prior art was micromachined from silicon using deposition and etching steps referred to as surface micromachining in the art. The manner of energizing the rotor is via a variable-capacitance, side-drive arrangement, wherein stator poles are arranged about the periphery of the rotor. By appropriate energization of the side-deposited stator poles using a multi-phase signal, rotation of the rotor is achieved.
The existing micromotor comprises a typical center-pin bearing side drive micromotor. In this side-drive design, torque is derived via position-dependent capacitance between the rotor and stator poles. However, because of the side-by-side arrangement of the rotor and stator poles, field coupling is less than optimal and, as a result, the torque characteristics of the motor suffer. Furthermore, twelve stators surrounding the perimeter of the 8-pole rotor connected to the center-pin bearing make access to the rotor difficult. The rotor itself does not allow transmission of power off its perimeter because gear teeth cannot be used. Also, the center pin about which the rotor rotates is fixed and cannot serve as a shaft for power take-off.
Thus, there is an existing need for a micromotor/engine design that will provide direct output mechanical power directly to micromechanisms without interference from the structure of the micromotor.